Grief Prevention is a plug-in that aims to add protection to the users from Griefers. It adds a series of changes to the game, most of which I will not mention here. Check out the Bukkit web site in the above link for ful information.

The most notable feature of this plugin for the users is the ability to claim land. Meaning a user can mark off an area of the world as their's, which will prevent other people from making any modifications to it. People can still enter the marked off area, but they will not be able to place or beak any blocks.